The wumpus-tree package

Draw trees represented by Data.Tree, output SVG or EPS. The
output should be quite good - no overlapping edges, identical
subtrees should have the same shape, leaf nodes evenly spaced.

Note - the demos now use font metrics. Font metrics for the
"Core 14" PostScript fonts are distributed as *.afm files
with GhostScript (AFM file version 2.0 for GhostScript 8.63) or
available from Adode (AFM file version 4.1). To run the demos
properly you will need one of these sets of metrics.

Changed the specification of trees so that they are built in a
monad. The bind operation of the monad allows anchors to be
extracted from tree nodes so they can be annotated with
supplementary graphics. At the moment this is rather limited
as Wumpus-Basic and Wumpus-Drawing do not offer much support
for anchors other than the basic type classes.

Changed the type of the rendering functions so they produce a
TreeDrawing. This type is more suitable for building composite
pictures than the previous type TreePicture.

Also the rendering functions now take a start point for the
root node, again this should be more convenient for drawing
composite pictures - see the demo which now draws all the
example trees on one page.

Internally the tree design is now more flexible - trees can be
designed upwards or leftwards rightwards, rather than just
downwards; and edge drawing style is lifted out of the
rendering to use a supplied combinator. Currently these
features are not exposed by the API, the API needs more
thought (possibly warranting changes to Wumpus-Basic and
Wumpus-Drawing).